Aims of the study: To estimate and compare the accuracy and precision of GFR-estimating equations based on the MDRD equation and three CKD-EPI equations using either creatinine or cystatin C or a combination of both in people with stage 3 CKD.

Study design: Multi-centre UK prospective longitudinal cohort study.

Sample size: 1320 participants will be recruited over 30 months.

Study Duration: The accrual period is for 30 months and all patients in the main study will be followed up for 3 years. The end of trial will be 6 months after the last data capture. The total study duration is 78 months.

Timeframes: NIHR HTA grant start date: 1st August 2013. Study set up will take place in 6 months, recruitment will take 30 months, all patients will be followed up for 36 months and 6 months has been allocated for data analysis and report writing.